German tenancy law tightly regulates how much a landlord can raise the rent. To check whether a demand is lawful, three building blocks matter: the Kappungsgrenze (cap), the local reference rent (Mietspiegel) and — if the building was modernised — the modernisation surcharge under §559 BGB. Our rent increase calculator computes all three instantly.
The three core rules
- §558 BGB cap (Kappungsgrenze): at most +20 % over 3 years (15 % in tight markets).
- §558 BGB reference rent: the new rent can never exceed the local reference rent (Mietspiegel).
- §558 (1) BGB 15-month block: at least 12 months since the last increase plus 3 months consent window.
The formula
Maximum new rent = min(current cold rent × (1 + cap %), local reference rent)
Maximum increase = new rent − current cold rent
20 % or 15 % cap?
Default cap is 20 % over 3 years. Each German state can lower the cap to 15 % by decree for cities with a tight housing market. Affected cities include Berlin, Munich, Hamburg, Cologne, Frankfurt, Stuttgart and Düsseldorf — the exact list depends on state regulation.
Local reference rent (Mietspiegel)
The reference rent is published in the qualified Mietspiegel per city, broken down by construction year, size, location and amenities. Rough 2026 figures:
- Berlin: ~ €11/m²
- Munich: ~ €21/m²
- Hamburg: ~ €14/m²
- Cologne / Düsseldorf: ~ €13/m²
- Frankfurt: ~ €16/m²
- Leipzig: ~ €8/m²
- Rural areas: ~ €7–10/m²
Worked example
70 m² flat in Cologne, current cold rent €800, Mietspiegel €13/m², cap 15 % (tight market).
- Current rent/m²: 800 ÷ 70 = €11.43/m²
- Local reference rent: 13 × 70 = €910
- Cap upper bound: 800 × 1.15 = €920
- Legal maximum (lower of the two): €910
- Maximum increase: 910 − 800 = €110
Modernisation surcharge (§559 BGB)
If the building was modernised — energetic refurbishment, new heating, lift, value-adding improvements — the landlord can add 8 % of the investment per year to the annual rent. Example: €15,000 modernisation × 8 % = €1,200/year = €100/month.
Hardship clauses (§559 (4) BGB) protect tenants if the increase would overwhelm them economically.
15-month block
At least 12 months must pass between increases (§558 (1) BGB). Adding 2 months for the tenant's review and 1 month for consent yields the effective 15-month block until the new rent applies.
Related calculators
- Rental Income Tax Calculator — German tax on rental income (§21 EStG)
- Rental Yield Calculator — gross and net rental property yield
- Home Loan Calculator — finance the property for renting or own use
FAQ
How much can a German landlord raise the rent?
At most +20 % (standard) or +15 % (tight markets) over 3 years — and never above the local reference rent.
What is the 15 % cap?
In tight housing markets the cap drops from 20 % to 15 % under §558 (3) sentence 2 BGB. Each Bundesland publishes the list.
How often can the rent be raised?
At least 12 months between increases (§558 (1) BGB) — plus 3 months for tenant consent = an effective 15-month block.
What is the modernisation surcharge?
Under §559 BGB, 8 % of the modernisation investment per year can be added to the annual rent.
Where do I find the local Mietspiegel?
Published by the city — also via tenants' associations (Mieterbund) and landlord associations (Haus & Grund).